This invention relates to a variable speed pumping-up electrical power system including a rotary electrical machine and a frequency converter connected to an a.c. power system, and more particularly to an electrical power system of the type described above in which the electrical machine can be operated at a rotation speed independent of the frequency of the a.c. power system.
A prior art, fixed speed pumping-up electrical power system has a problem in that its load cannot be regulated when its pump/turbine is placed in a pumping operation mode. In a pumping-up electrical power system using, for example, a synchronous machine, an input determined by the rotation speed of the synchronous machine is applied to the pump/turbine when the pump/turbine is placed in its pumping operation mode, and no function for regulating the input power from the a.c. power system is provided. Therefore, researches and studies have been made in which an induction machine provided with a secondary exciter is used in place of the synchronous machine to permit load regulation. For example, the principle of load regulation was stated in a paper entitled "Researches and Developments of Variable Speed Pumping-up Electrical Power System" reported in Joint Convention of Kansai Branch of the Institute of Electrical Related Engineers of Japan in 1985. However, no practical method for load regulation was reported in the convention.